Formulation for use in chrome or chrome-free tannage

ABSTRACT

A formulation for use in chrome-free or chrome tanning is proposed, comprising a clay mineral which, after vigorous stirring for 30 minutes in water at 50° C., has a number average particle diameter of less than 2 μm or a bimodal size distribution with a first, finely divided fraction whose number average particle diameter is less than 0.5 μm and a second, coarser fraction whose number average particle diameter is less than 5 μm, determined in each case by the method according to ISO 13320-1, by combined laser light diffraction and light scattering, the amount of the first, finely divided fraction being from 10 to 90% by weight, and one or more substances from one or more of the following groups: organic polymers, aldehyde tanning agents, sulfone tanning agents, resin tanning agents, phenol tanning agents, fatliquoring agents, vegetable tanning agents, dyes and pigments.

The present invention relates to a formulation for use in chrome-freeand chrome tanning, comprising a clay mineral, and a use of clayminerals.

In tanning, readily perishable animal hide substance is processed bypreparatory treatment with tanning assistants, chemical reaction withtanning agents and appropriate finishing to give resistant leather whichremains soft and supple and has the desired performance characteristics(cf. Römpp Chemie Lexikon, 9th edition, 1995, page 1538). The high watercontent stabilizing the collagen structure of the original hidesubstance is reduced thereby and irreversible stabilization is realizedby crosslinking by means of tanning agents. A distinction is madebetween inorganic, mineral and organic chemical tanning agents.Inorganic tanning agents are mainly chromium(III) salts, polyphosphatesand aluminum, zirconium and iron salts. Organic tanning agents may be ofsynthetic or vegetable origin (cf. Römpp Chemie Lexikon, 9th edition,page 1541).

Inorganic polymers have been known to date in tanning as a rule asfillers. According to the opinion described in H. Herfeld: Bibliothekdes Leders, Volume 3, Umschau Verlag, Frankfurt, 2^(nd) edition, 1990,page 237, inorganic fillers have no tanning effect. These includekaolin, finely divided clay (china clay), colloidal silica, etc. Theseproducts are deposited in the loosely structured main parts andpreferably in the flesh side. There is very little effect on the grainstructure, the buffability is often improved and the plush is shorter.

However, the disadvantage here was that the very loose binding or thesuperficial incorporation in the hide substance. In subsequent processsteps of leather production, for example milling, a considerableproportion of incorporated substances was therefore liberated again andled to clogging of the grain or to abrasive damage to the grainstructure.

DE-C 969689 describes the use of surface-active silicon-containingfillers, in particular of silica and/or of silicates in colloidal form,having a particle size of from 0.1 to 1 μm, for leveling, shortening andrefining the buffed surface of in particular suede leathers. Thesesilicon-containing colloid dusts are intended to be strongly absorbed onthe collagen fibers, with the result that the incorporation is to besubstantially maintained even during subsequent operations. However,colloidal silica, silicates or mixtures thereof have the disadvantage,as dynamic systems, of being subject to continuous change. During thischange, an increase in the size of the initially incorporated particlesto give sand-like agglomerates occurs during storage or during the useof the leather/leather goods owing to Ostwald ripening. Consequently,abrasive damage to the leather is caused for example in the walkingcreases of upper leathers by drumming. This silicate tanning istherefore considered to be comparatively unstable.

The technical article by Y. Lakshminarayana et al. in JALCA 97 (2002),14 to 21, describes the use of bentonites for the preparation of graftpolymers with methacrylic acid for use in tanning, in particular in theaftertreatment of chrome-tanned leather.

It is an object of the present invention to provide a stable formulationcomprising a clay mineral for use in chrome-free and chrome tanning,which formulation ensures improved properties of the leather obtainedthereby and an improvement in the process.

We have found that this object is achieved by a formulation for use inchrome-free and chrome tanning, comprising a clay mineral which, aftervigorous stirring for 30 minutes in water at 50° C., has a numberaverage particle diameter of less than 2 μm or a bimodal sizedistribution with a first, finely divided fraction whose number averageparticle diameter is less than 0.5 μm and a second, coarser fractionwhose number average particle diameter is less than 5 μm, determined ineach case by the method according to ISO 13320-1, by combined laserlight diffraction and light scattering, the amount of the first, finelydivided fraction being from 10 to 90% by weight, and one or moresubstances from one or more of the following groups: organic polymers,aldehyde tanning agents, sulfone tanning agents, resin tanning agents,phenol tanning agents, fatliquoring agents, vegetable tanning agents,dyes and pigments.

It has surprisingly been found that the use of clay minerals which,after delamination by vigorous stirring in warm water, have a numberaverage particle diameter of less than 2 μm or a bimodal sizedistribution with a first, finely divided fraction whose number averageparticle diameter is less than 0.5 μm and a second, coarser fractionwhose number average particle diameter is less than 5 μm, the amount ofthe first, finely divided fraction being from 10 to 90% by weight, astanning agents or for the preparation of tanning agents leads to asubstantial improvement in the properties of the leather obtainedthereby. A treatment with a sufficient amount, as a rule about 950 ml,of water, based on 50 g of the clay mineral, at 50° C. with vigorousstirring, for example at 250 rpm, for 30 minutes is required fordelamination for the determination of the number average particlediameter, the clay mineral being dispersed in the water. This treatmentis intended to ensure that the clay mineral is delaminated until theparticle size no longer changes.

The particle sizes and particle size distribution were determinedaccording to ISO 13320-1 by combined laser light diffraction and lightscattering using a Malvern 2000 analysis instrument from Malvern.

It is assumed that the interaction of the clay minerals with thecollagen chains of the hide is essential for the action of the clayminerals having the particle sizes defined above. This interaction ispossible, for example, via hydrogen bridges between collagen and thesurface hydroxyl groups of the clay minerals. It has surprisingly beenfound that clay minerals having the defined particle sizes areirreversibly incorporated in the hide.

Clay minerals are weathering products of primary aluminosilicates, i.e.of compounds comprising different proportions of alumina and silica.Silicon is surrounded tetrahedrally by four oxygen atoms, while aluminumis present in octahedral coordination. Clay minerals very predominantlybelong to the phyllosilicates, also referred to as sheet silicates orleaf silicates, but in some cases also to the band silicates (cf. RömppChemie Lexikon, 9th edition, 1995, pages 4651 and 4652).

For the novel formulations, it is particularly advantageous if the claymineral is a phyllosilicate. The phyllosilicate may preferably be akaolinite, muscovite, montmorillonite, smectite or bentonite, inparticular a hectorite.

Particularly good results are obtained if substances which, owing totheir chemical structure, are capable of forming strong hydrogen bridgebonds with the clay minerals, in particular urea or urea derivatives,alcohols, polyols, propylene carbonate, organic amides, urethanes,saccharides or derivatives of saccharides, in particular nitrocellulose,sulfite cellulose or ethylhexylcellulose, are added to the clay mineralsbefore or during the use thereof as tanning agents. By means of thistreatment, inter alia, delamination of the clay mineral, in particularsheet silicate, is promoted.

Organic polymers which may be used in the novel formulations are, forexample, polymethacrylates, polyacrylates, maleic anhydride/styrenecopolymers or maleic anhydride isobutene copolymers.

Formulations wherein the clay mineral has a number average particlediameter of less than 1 μm are preferred.

A formulation comprising a clay mineral which, after vigorous stirringfor 30 minutes in water at 50° C., has a number average particlediameter of less than 2 μm or a bimodal size distribution with a first,finely divided fraction whose number average particle diameter is lessthan 0.5 μm, determined by the method according to ISO 13320-1, bycombined laser light diffraction and light scattering, and a second,coarser fraction whose number average particle diameter is less than 5μm, the amount of the first, finely divided fraction being from 10 to90% by weight, is particularly suitable and the aldehyde tanning agentis glutaraldehyde or a derivative of glutaraldehyde, in particular anacetal.

The present invention also relates to a use of clay mineral which, aftervigorous stirring for 30 minutes in water at 50° C., has a numberaverage particle diameter of less than 2 μm or a bimodal sizedistribution with a first, finely divided fraction whose number averageparticle diameter is less than 0.5 μm and a second, coarser fractionwhose number average particle diameter is less than 5 μm, the amount ofthe first, finely divided fraction being from 10 to 90% by weight, astanning agents or for the preparation of tanning agents.

The use of clay minerals having a number average particle diameter ofless than 1 μm is preferred.

A use wherein substances which, owing to their chemical structure, arecapable of forming strong hydrogen bridge bonds with the clay mineral,in particular urea or urea derivatives, alcohols, polyols, propylenecarbonate, organic amides, urethanes, saccharides or derivatives ofsaccharides, in particular nitrocellulose, sulfite cellulose orethylhexylcellulose, are added to the clay minerals before or during theuse thereof as tanning agents is advantageous.

The clay mineral used is preferably a phyllosilicate, particularlypreferably a kaolinite, muscovite, montmorillonite, smectite orbentonite, in particular a hectorite.

Said clay minerals can preferably be used by employing them as tanningagents or for the preparation of tanning agents for preliminary tanning,in particular for chrome-free preliminary tanning.

Further preferred use is one wherein the clay minerals are used astanning agents or for the preparation of chrome or chrome-free tanningagents for retanning.

The following advantages are achieved with the novel formulations and bythe novel use:

In particular, a significantly improved selective filling effect isachieved, i.e. loose regions are preferably filled, with the result thatan improvement in the leather quality and surface yield is achieved.

The grain tightness is considerably improved, i.e. creasing orspliceability on the surface is considerably reduced or avoided.

The leather quality is also increased by the improved embossability.

Moreover, the leather quality is improved by an increase in the tensilestrength.

An important quality feature in the preliminary tanning, in particularin the case of chrome-free leathers, is the shaveability of thesemifinished product. This is improved by the invention, resulting inimproved surface characteristics and a level thickness of the shavedhide and reduced tool wear, in particular knife wear, during the shavingprocess. The time gain owing to the improved processability due to thereduced adhesion of the shaving knife is also considerable.

According to the invention, the fat distribution of both natural andapplied fat is improved, resulting in a more even and more regularsurface. The improvement in the levelness of fat distribution moreovermakes it possible to save up to 50% of the fatliquoring agent in theretanning and thus to provide particularly environmentally compatibletanning processes with correspondingly low wastewater pollution.

A substantial disadvantage of the process is the significant improvementin the environmental compatibility by virtue of the fact that the liquorexhaustion, in particular with respect to the fatliquoring agent, isimproved by up to 50% with a correspondingly lower wastewater pollution.

The invention is explained in more detail below with reference toexamples:

EXAMPLES E1.1 TO E1.4 AND COMPARATIVE EXAMPLES C1.0 TO C1.4 PRELIMINARYTANNING OF WET WHITE

The trade grades mentioned below under their trade names are productsfrom BASF AG, Ludwigshafen.

Pickled hide strips split to a thickness of from 1.6 to 1.8 mm and eachweighing 250 g were treated together with 200 g of water in each case ata pH of 3.0 at 25° C. in succession with 3% of aqueous glutaraldehydesolution (Relugan® GT 24) for 60 minutes and then with 4% of the sulfonetanning agent Basyntan® SW. After a drumming time of 90 minutes, the pHwas increased to 3.8 to 4.0 with a mixture of 2 parts by weight ofTamol® NA and sodium formate.

In comparative examples C1 to C1.4 and examples 1.1 to 1.4, 10 g of theclay minerals mentioned in table 1 below were added in each case to theliquors together with the glutaraldehyde solution. The mean particlesizes of the clay minerals were determined by laser diffraction/lightscattering on freshly prepared suspensions having a solids content of 5%in each case, according to ISO 13320-1.

After the preliminary tanning, in each case 100 g of each liquor werecoarsely filtered through a 25 μm filter. The remaining solids contentwas sedimented in a centrifuge, washed, dried and then weighed.

Table 1 below shows the solids contents of the liquor after the tanningprocess, based in each case on the original total liquor. Theshaveability of the leather subjected to preliminary tanning was ratedon a scale from 1 to 5. The shrinkage temperature was determinedaccording to DIN 53336, which was modified in the following points asmentioned below:

-   -   Point 4.1: the specimen had the dimensions 3 cm·1 cm and the        thickness was not determined;    -   Point 4.2: instead of 2 specimens, only one specimen was tested        per leather sample;    -   Point 6: omitted;    -   Point 7: the drying in a desiccator under reduced pressure was        omitted and    -   Point 8: the shrinkage temperature was read when the pointer        moved back.

TABLE 1 Solids Mean content particle of Shrinkage size liquorShaveability temperature Clay mineral [μm] [g] [Rating 1-5] [° C.] C 1.0— — — 3 79 C 1.1 Kaolin 13.2 3.8 3.5 77 C 1.2 Kaolin 7.6 2.9 3 78 C 1.3Kaolin 5.1 2.7 2.5 78 C 1.4 Kaolin 3.2 1.4 2.5 79 E 1.1 Kaolin 1.3 0.551.5 81 E 1.2 Montmorillonite 0.6 0.30 1 83 E 1.3 Kaolin/ bimodal 0.7 182 montmorillonite 0.6/3.2 E 1.4 Kaolin/ 0.2/1.3 0.35 1 82 bentonite

The comparison of the results of comparative experiments C1.0 to C1.4and of the examples according to the invention E1.1 to E1.4 shows asubstantial reduction in the solids content of the liquor after thetanning process (fourth column in table 1), i.e. a substantialimprovement in the liquor exhaustion, and an improvement in theshaveability (5th column) and the shrinkage temperature (last column).

COMPARATIVE EXAMPLES C2.0 AND C2.1 AND EXAMPLES E2.1 AND E2.2 RETANNINGOF WET BLUE UPPER LEATHER

A commercial Zebu wet blue leather was shaved to a thickness of from 1.8to 2.0 mm and divided into quarters. Thereafter, 2% of sodium formateand 0.4% of sodium bicarbonate as well as 1% of Tamol® NA were added tothe quarters in a drum and at a liquor length of 200%, i.e. a liquor of2 kg of aqueous phase to 1 kg of leather, at intervals of 10 minutes.After 90 minutes, the liquor was discharged and the Zebu quarters weredistributed over four separate drums.

In comparative example 2.0, a 1% strength aqueous solution of the dyeLuganil® brown was metered at 25° C. into one of the drums and the Zebuquarter was drummed for 10 minutes.

Thereafter, 3% of polymer tanning agent Relugan® RV, 5% of sulfonetanning agent Basyntan® DLX and 2% of resin tanning agent Relugan® DLFwere added and drumming was effected again for 20 minutes at 10 rpm.

Thereafter, the hide was treated for 40 minutes with 3% of commercialmimosa vegetable tanning agent and then for a further 40 minutes with 2%of mimosa vegetable tanning agent.

Acidification was then effected with formic acid to a pH of from 3.6 to3.8. After 20 minutes, the liquor was discharged and washing waseffected with 200% of water. Finally, 5% of Lipodermlicker® CMG and 2%of Lipodermlicker® PN were metered in 100% of water at 50° C. After adrumming time of 45 minutes, acidification was effected with 1% strengthformic acid.

The washed leather was dried and staked and the quality was assessedwith respect to body, grain tightness, softness and levelness of thedyeing/fatliquoring according to a rating system from 1 (very good) to 5(unsatisfactory). Moreover, the tensile strength in Newton according toDIN 53328 and the stitch tear resistance in Newton according to DIN53331 were determined. The comparison of the values for the chemicaloxygen demand (COD) confirms the improved liquor exhaustion with thenovel clay minerals.

In comparison with comparative example 2.0, in comparative example 2.1 aclay mineral corresponding to comparative example 1.1, i.e. kaolinhaving a further particle size of 13.2 μm, was metered in in aconcentration of 4% together with the sulfone tanning agent Basyntan®DLX.

In comparison, in each case 4% of the clay minerals corresponding toexamples E1.1 and E1.4 were metered in in examples E2.1 and E2.2.

Table 2 below shows a substantial quality improvement with respect tobody, grain tightness, softness, levelness of the dyeing/fatliquoringand with respect to tensile strength and stitch tear resistance of theleathers obtained in examples E2.1 and E2.2 according to the inventioncompared with comparative examples C2.0 and C2.1.

TABLE 2 Stitch Levelness Tensile tear Dyeing/ COD Clay Grain strengthresistance Fatliquorin [mg O₂/l mineral Body tightness Softness [N] [N]g liquor] C 2.0 — 3 3.5 3 428 302 3 16 200 C 2.1 C 1.1 3 3 3.5 410 2922.5 14 800 E 2.1 E 1.1 2 2.5 2 452 319 1 10 700 E 2.2 E 1.4 1.5 2 2.5449 328 1.5  6 900

COMPARATIVE EXAMPLES C3.0 TO C3.2 AND EXAMPLES 3.1 TO 3.3 RETANNING OFWET WHITE FURNITURE LEATHER

A Southern German cattle hide was converted into a wet whitesemifinished product, shaved to a thickness of 1.2 mm and cut intostrips of about 250 g each.

In comparative example C3.0, the hide was treated for 40 minutes at 35°C. with 150% of water containing 3% of Relugan® GT 50, i.e. aformulation which substantially comprises an aqueous glutaraldehydesolution, and 0.5% of formic acid. Thereafter, treatment was effectedfor 60 minutes with 4% of a mixture consisting of equal parts of Tamol®NA and sodium formate and then drumming was effected with 4% of Relugan®SE and 5% of Basyntan® SW, i.e. sulfone tanning agent, for 20 minutes.Thereafter, 6% of the commercial vegetable tanning agent Tara and 2% ofresin tanning agent Relugan® S and 2% of the dye Luganil® brown NGB weremetered in and the mixture was drummed again. After 2 hours, the pH wasbrought to 3.6 with formic acid. The fatliquoring components added were6% of Lipodermlicker® CMG and 1% of Lipamin® OK. After a drumming timeof a further 60 minutes, acidification was once again effected withformic acid to pH 3.2 and, before the liquor was discharged, samples forthe determination of the solids content thereof, i.e. the liquorexhaustion, were taken. The leathers were washed twice with 100% ofwater each time, stored moist overnight and, after partial drying, driedon a toggle frame at 50° C.

The liquor exhaustion and quality of the leather with respect to body,grain tightness, softness, levelness and embossing were rated accordingto a rating system from 1 (very good) to 5 (unsatisfactory). Theassessment of the liquor exhaustion was effected visually according tothe criteria of residual dye (extinction) and turbidity (fatliquoringagent). For assessing the embossing, the leather pieces were treated bythe following procedure: finished and pressed with a platen press at 120bar and from 80 to 100° C. for 5 seconds. The quality of the embossingwas measured according to the criteria of embossing depth, levelness andmemory after tensile loading.

No clay mineral was added in comparative example C3.0, the clay mineralcorresponding to C1.1 was added in comparative example C3.1, i.e. kaolinhaving a mean particle size of 13.2 μm, and the clay mineralcorresponding to comparative example C1.3 was added in comparativeexample C3.2, i.e. kaolin having a mean particle size of 5.1 μm.

The clay mineral corresponding to example E1.1 was added in exampleE3.1, i.e. a kaolin having a mean particle size of 1.3 μm, a claymineral corresponding to example E1.2 was added in example 3.2, i.e.montmorillonite having a mean particle size of 0.6 μm, and the claymineral corresponding to example E1.3 was added in example E3.3, i.e. amixture of kaolin and montmorillonite having a bimodal mean particlesize distribution, one fraction having a mean particle size of 0.6 μmand a second fraction having a mean particle size of 3.2 μm.

TABLE 3 Stitch Tensile tear Clay Liquor Grain strength resistancemineral exhaustion Body tightness Softness [N] [N] Levelness Embossing C3.0 — 3.0 3 3.5 3 268 192 3 3 C 3.1 C 1.1 4 3 3 3.5 248 188 2.5 3.5 C3.2 C 1.3 3.5 2.5 2.5 3 259 194 2 3 E 3.1 E 1.1 2.5 2 2.5 2 277 201 12.5 E 3.2 E 1.2 2 2 1.5 2 284 223 1 1.5 E 3.3 E 1.3 1.5 1.5 2 2.5 289218 1.5 1.5

The comparison of the results of comparative examples C3.0 to C3.2 andof the examples according to the invention E3.1 to E3.3 in table 3 showsan improvement in all quality features, i.e. body, grain tightness,softness, tensile strength, stitch tear resistance, levelness, embossingand liquor exhaustion.

1. A method for chrome-free and chrome tanning, comprising contacting ananimal hide with a formulation comprising: a clay mineral, which, aftervigorous stirring for 30 minutes in water at 50° C., has a numberaverage particle diameter of less than 2 μm, or a bimodal sizedistribution with a first, finely divided fraction, whose number averageparticle diameter is less than 0.5 μm, and a second, coarser fraction,whose number average particle diameter is less than 5 μm, determined ineach case by the method according to ISO 13320-1, by combined laserlight diffraction and light scattering, and wherein, the amount of thefirst, finely divided fraction is from 10 to 90% by weight; and one ormore substances selected from the group consisting of organic polymers,aldehyde tanning agents, sulfone tanning agents, resin tanning agents,phenol tanning agents, fatliquoring agents, vegetable tanning agents,dyes, pigments and mixtures thereof, wherein the clay mineral is aphyllosilicate selected from the group consisting of kaolinite,smectite, muscovite, montmorillonite, bentonite, hectorite and mixturesthereof.
 2. The method as claimed in claim 1, wherein the clay mineralis muscovite.
 3. The method as claimed in claim 1, wherein the claymineral is hectorite.
 4. The method as claimed in claim 1, wherein saidformulation comprises a clay mineral, which, after vigorous stirring for30 minutes in water at 50° C., has a number average particle diameter ofless than 2 μm determined by the method according to ISO 13320-1, bycombined laser light diffraction and light scattering.
 5. The method asclaimed in claim 4, wherein the clay mineral has a number averageparticle diameter of less than 1 μm.
 6. The method as claimed in claim4, wherein said formulation further comprises one or more substances,which, owing to their chemical structure, are capable of forming stronghydrogen bridge bonds with the clay mineral.
 7. The method as claimed inclaim 6, wherein the one or more substances which, owing to theirchemical structure, are capable of forming strong hydrogen bridge bondswith the clay mineral, are selected from the group consisting of urea orurea derivates, alcohols, polyols, propylene carbonate, organic amides,urethanes, saccharides or derivatives of saccharides, nitrocellulose,sulfite cellulose, ethylhexylcellulose, and mixtures thereof.
 8. Themethod as claimed in claim 1, wherein the one or more substances areselected from aldehyde tanning agents, and wherein the aldehyde tanningagents are glutaraldehyde or a derivative of glutaraldehyde.
 9. Themethod as claimed in claim 1, wherein the clay mineral has a numberaverage particle diameter of less than 1 μm.
 10. The method as claimedin claim 1, wherein the phyllosilicate is selected from the groupconsisting of kaolinite, montmorillonite, bentonite, and mixturesthereof.
 11. The method as claimed in claim 1, wherein said animal hideis a tanned animal hide.
 12. The method as claimed in claim 1, whereinsaid formulation comprises: a clay mineral, which, after vigorousstirring for 30 minutes in water at 50° C., has a bimodal sizedistribution with a first, finely divided fraction, whose number averageparticle diameter is less than 0.5 μm, and a second, coarser fraction,whose number average particle diameter is less than 5 μm, determined ineach case by the method according to ISO 13320-1, by combined laserlight diffraction and light scattering, and wherein, the amount of thefirst, finely divided fraction is from 10 to 90% by weight.
 13. Themethod as claimed in claim 12, wherein said formulation furthercomprises one or more substances, which, owing to their chemicalstructure, are capable of forming strong hydrogen bridge bonds with theclay mineral.
 14. The method as claimed in claim 13, wherein the one ormore substances which, owing to their chemical structure, are capable offorming strong hydrogen bridge bonds with the clay mineral, are selectedfrom the group consisting of urea or urea derivates, alcohols, polyols,propylene carbonate, organic amides, urethanes, saccharides orderivatives of saccharides, nitrocellulose, sulfite cellulose,ethylhexylcellulose, and mixtures thereof.